For computer monitors that are mostly non-interlaced or progressive type display devices, video images or graphic images must be displayed by sequentially displaying each successive line of pixel data sequentially for a frame of an image. In contrast, inter-laced display devices, such as conventional television displays, typically display images using even and odd line interlacing.
The process of producing one progressive frame on every incoming interlaced field is called de-interlacing. When such interlaced signals are received for display in a progressive display, such as a computer display or other suitable display, picture quality problems can arise especially when motion is occurring in the picture where inferior methods of de-interlacing are used.
Two interpolation techniques are often involved in de-interlacing, these are temporal interpolation and spatial interpolation. Temporal interpolation creates the missing pixels using pixels that were incorrect in time but have the correct spatial coordinates. Temporal interpolation (e.g. weave) is typically best suited if the video sequence consist of static images but does not work well with moving video. Spatial interpolation (e.g. bob) creates missing pixels using pixels that are correct in time but have incorrect spatial coordinates. Techniques vary from simply averaging the pixels above and below the missing pixel to more elaborate methods that utilize many nearby pixels in order to derive edge orientation and reproduce edges without jagged artifacts. It is also known to control a blend of spatial versus temporal interpolation along, for example, edges of detected motion.
In the deinterlacing process, interlaced video with moving ticker symbols, such as those that are scrolled across the bottom or top of a display screen to indicate stock market ticker symbols and stock prices, can suffer from resolution degradation due to the blending from neighboring pixels to fill the missing pixels in the current field. Furthermore, the degradation is highly noticeable because viewers are interested at tracking the text in motion. One type of deinterlacing technique, sometimes referred to as motion adaptive deinterlacing, does not use motion vector detection, it uses multiple fields and attempts to determine the presence of movement, but not the direction or speed of movement for example. In addition, another technique sometimes referred to as motion correct deinterlacing attempts to detect the direction of motion and the speed of the motion, however it is typically done on a block by block basis. Such motion estimation techniques can require large amount of computation. Other techniques may employ, for example, the use of a two dimensional search window to get a coarse level of motion detection such as, for example, starting with a 16×16 pixel block and if motion is detected within the block then an iterative approach searches for motion in 4×4 pixel sub-blocks. Again, this technique can be expensive to implement and can take large amount of time due to the iterative nature of the process. Also one or more of the above techniques may attempt to analyze motion in an entire field or frame whereas horizontal moving ticker symbols may only be located in the upper or lower one third of a viewing area.
Accordingly, a need exists for a method and apparatus that overcomes one or more of the above problems.